Senseless filtering, and how to avoid it

So, there's an annoying intercepting proxy which won't let you read
stuff that looks interesting. What are you going to do about it? If
you're me, you invent a ghastly thing out of bits of string and
sellotape, and then have enough temerity left over to suggest that
other people might want to use it too.

What do you need?

You need a browser with enough clue to be able to use a proxy
autoconfigure script. That's pretty much any e-sewer browser since
Netscape Navigator, but don't expect w3m to be able to use it.

The hack here has three parts.

There's a gobbet of Javascript which is a proxy autoconfigure
script. (An autoconfigure script defines a Javascript function which
is given a URL and is expected to output a list of proxies to try.)

There's a shell script which you're meant to wire up to a
port-forwarder thingummy such as netcat or fwd.
When you've done this, it implements the world's worst HTTP proxy.

You'll need a friendly HTTP proxy that you can talk to.

I'm assuming that the HTTP proxy is friendly, but is slow and/or
reluctant to carry seriously high volumes of stuff, so that it's a
last resort rather than something you can just configure your browser
to use by default for everything.

How does this work?

I'm so glad you asked me that. Here's what happens when you try to
fetch a naughty resource.

The browser gives the URL to the proxy configuration script. It
doesn't know anything special about this URL yet, so it returns its
default proxy, which is probably a direct connection.

The Senseless intercepting proxy filter notices that you've asked
for something naughty. It makes a mental note of this, and